Transformer



y 1939- M. SCHWAIGER v 2,157,922

TRANSFORMER Filed June 24, 1938 INVENTOR MOX5C WO/Q'ef,

WITNESSES:

Patented May 9, 1939 UNITED STATES TRANSFORMER Pennsylvania Application June 24, 1938, Serial No. 215,552 In Germany July 10, 1937 of preferred embodiments thereof, reference bing made to the accompanying drawing, in which:

4 Claims.

This invention relates to transformers and particularly to control apparatus for governing the operation of tap changing equipment for transformers.

s In many transformer installations, it is desirable to provide tap changing mechanism for varying the effective number of turns of a transformer winding to vary the voltage ratiobetween the primary and secondary circuits connected to the m transformer.

cludes tap selecting switches arranged to be operated under no-load current to select the desired tap through which the circuit conductor is to be connected to a transformer winding, the interrup- 15 tion of the load current being effected by a separate load current interrupting switch adapted to be operated under load. The tap selecting switches and the load circuit interrupting switches are operated in a desired sequence in a well-known manner by electric motors or by other means to effect operation of the tap changing equipment from one tap connecting position to another tap connecting position.

Frequently such tap changing equipment or regulating mechanism is provided with automatic means by which a tap changing operation once started continues automatically, independently of power circuit conditions, in an attempt to maintain the desired voltage on the secondary or output side of the transformer. The source of energy for driving the tap changing motor is in many cases independent of the energy supplied through the transiormer to the power circuit; that is, the electric motor may be driven, for example, from a source of energy at the power station, such as a storage battery. If, during the operation of a transformer tap changer mechanism, a short circuit or a heavy overload occurs on the power system, the tap changing mechanism will be required to operate through a considerable number of steps in an attempt to maintain the desired voltage under conditions in which the switching mechanism may be destroyed or a seriously damaged by the heavy overload currents.

It is an object of this invention to avoid these disadvantages by providing a protective mechanism operated in response to overload currents for interrupting the operation of a transformer tap changer mechanism upon the occurrence of a predetermined overload of the transformer circuit.

Other objects and advantages of the invention will be apparent from the following description The tap changing mechanism in-- Figure l is a schematic illustration oi changing mechanism embodying the invention; Figs. 2 and 3 are schematic views illustrating the connection of load current interrupting switches of the tap changer mechanism in intermediate positions; and

Fig. 4 is a schematic illustration of circuits and apparatus comprising a tap changing mechanism having a continuously moving load circuit interrupting switch, such as shown in Figs. 2 and 3, together with auxiliary apparatus for pre-- venting the load switch from stopping in certain intermediate positions.

Referring to the tap changing mechanism illustrated in Figure 1, a regulating transformer i is shown having three phase primary windings 3 connected to power circuit conductors 2 and secondary windings 4, selected tap points of which are connected to power circuit conductors through taps 5 and switching mechanism which is here illustrated for one phase winding only in order to simplify the illustration of the invention.

The taps 5 are connected to fixed selector switch contacts 6 that are adapted tobe engaged by movable selector switch contacts "i and 8 that are connected by means of conductors 9 and 12, respectively, to load switch contact members l3 and i l that are adapted to be engaged by movable load switch contact members it and H, respectively, both of which are connected to The movable load switch contact member i6 is carried on a lever l8, the lower end of which is pivotally mounted on a pin l9, and the contact member I? is mounted on a lever 22, the lower end of which is pivoted on a pin 23. The upper ends of the levers I8 and 22 are connected by a link 25 to form a toggle mechanism actuated by a spring 26, one end of which is connected to a point on the link 25 intermediate its ends, and the other end of the spring is connected to a crank 21 that is operated by a shaft 28 through mechanism including a clutch 29 and a motor 32. The motor 32 has an armature winding 33 that is supplied with energy through conductors 3d and 35, and difierentially related field windings 36 and 31, the outer terminals of which are connected to one side of a source of energy through conductors 38 and 39, respectively, and the common terminal of which is connected to the other terminal of the source of energy through conductor 42, switch member 43 in its circuit closing position and conductor The motor 32 may be arranged to operate each of three load circuit switches corresponding to the illustrated toggle operated switch, one load circuit switch being associated with each of the three phase windings 4 of the transformer, and to also operate the tap selecting contacts I and 8 associated therewith in a predetermined sequence in a well-known manner through a wellknown mechanism (not shown). Current transformers are provided, the primary windings 45 of which are shown in each of the phase conductors 2, each of which may be associated with a secondary winding 46 for energizing the winding 41 to operate the switch 43 to its circuit interrupting position upon a predetermined overload current in a phase conductor of the transformer as determined by the setting of the rheostat 48.

In the operation of the mechanism shown in Fig. 1, a predetermined movement of the motor 32 moves the one or the other of the contact members I or 8 through which the circuit is temporarily interrupted along the row of fixed contact members 6 into engagement with the selected one adjacent to that through which the circuit is passing, and through which it is desired to transfer the power circuit. After the movable tap selector contact 'I or 8 has been thus moved to its new position, the load circuit interrupting switch is operated by the motor 32 to such position that the spring 26 moves from the one to the other side of the axes of the toggle mechanism, thus causing the switch to operate with a snap action from one circuit closing position to the other circuit closing position. In the illustrated position of the mechanism of Fig. 1, the load circuit is completed through selector contact I, conductor 9,. contact members I3 and I6 of the load switch to line conductor I5. After operation of the selector contact 8 to its illustrated position and continued operation of the motor, the crank 21 will be moved to the right, as viewed in Fig. 1, until the bias of the spring 26 is in a direction such that the levers I8 and 22 carrying contact members I6 and I1, respectively, will be moved abruptly to the right, interrupting the circuit through contacts I3 and I6 and closing the circuit through contacts I4 and I1.

If, after the motor has been set in operation, a short circuit or a heavy overload current passes through the conductors 2 such that the continued operation of the mechanism from one tap position to the next might damage the switch contact members, the energization of the winding 5 41 of the circuit interrupting switch 43 actuates the switch 43 to its illustrated position to prevent further operation of the motor 32 until the overload or fault current has disappeared in the power circuit.

In many tap changing mechanisms, the load circuit interrupting switches are not arranged to be operated with a snap action as in Fig. 1, but may be a relatively slow moving switch connected to move in accordance with the movement of the shaft of the motor driving the tap changing mechanism through gears or otherwise, and which mechanism must not remain at rest in certain positions, such, for example, as illustrated in Figs. 2 and 3. In Figs. 2 and 3, a movable load interrupting switch contact member 52 that is primarily connected to a line circuit conductor 53 is adapted to engage one or two adjacent contact members 54, 55, 56 or 51, contact members 54 and 51 of which are connected by conductor 58 to the selector switch contact 8 corresponding to that shown in Fig. 1, and contact members 55 and 56 that are connected to each other through a resistor 59 are connected by conductor 62 to a tap selector contact 1 similar to that shown in Fig. 1. Should the contact member 52 stop in the position shown in Fig. 2, so that a short space exists between contact members 52 and 56, an are 64 might be formed which is undesirable. Also, should the contact member 52 stop in the position shown in Fig. 3, an are 65 might be formed between contact members 52 and 55, which is likewise undesirable.

Fig. 4 shows a tap changing mechanism provided with an auxiliary device for preventing the motor operating the tap changing mechanism from stopping when the contact member 52 is in certain positions in its travel. In Fig. 4, the tap changing motor 32 operates a shaft 63 that moves the tap changing contact member 52 and that also operates contact discs 66 and 61. Fixed contacts 68 and 69 are provided for engaging the discs 66 and 61, respectively, and are connected to switch contact members I2 and I3, respectively, that are adapted to be engaged by a movable contact member I4 carried by a lever I5 and actuated by a cam disc I6 in a manner to be later explained. In the illustrated position of the equipment a circuit is completed in shunt relation to the circuit interrupting switch 43 through conductor 11, contact I8, collector ring I8, conductor 82, the contact members 83, 68, I3, and I4 and conductor 84.

The position of the contact member 52 shown in Fig. 4 corresponds to that shown in Fig. 3, in

which the switch contact 43 is paralleled by the circuit just above traced. When the contact member 52 is in the position illustrated in Fig. 2, a similar circuit will be closed through contact member 85 on the contact disc 61 and contact member 69. It will be noted that when the tap changing mechanism is in a tap position, the

cam 16 is in such position that the roller 8.6 is

within the opening 81, and the contact member I4 is in a mid-position out of engagement with either the contact I3 or the contact 12.

In the position of the equipment illustrated in Fig. 4, the tap changing mechanism has been operated from this tap or stationary position a slight distance until the roller 86 is riding on the outer surface of the cam I6 in a direction to force the contact member 14 into engagement with the contact member I3 to complete the circuit above traced. If the mechanism is operated in a reverse direction, the cut-away portion 81 in the surface of the cam I6 will move in the opposite direction so that the roller 81 will be moved upwardly toward the left, and the contact member I4 will be brought into engagement with the contact member T3 to complete a circuit in shunt relation with the switch 43 through the fixed contact member 68 and the one or the other of the contact members 89 or 92 carried on the contact cam 66 to prevent the movable contact member 52 from stopping in an undesired position such that arcs therefrom to one of the adjacent fixed contact members might occur.

The detailed mechanism for effecting the desired sequence in operation of the load circuit interrupting switch contact member 52 and the selector switch contact members I and 8, which are of well-known construction, are omitted for the sake of simplicity.

Many changes in the details of construction illustrated and described will be apparent to those skilled in the art within the spirit of my invention, and I do not wish to be limited otherwise than by the scope of the appended claims.

I claim as my invention:

1. In a tap changing equipment for transformers, a transformer winding having a plurality of taps and a plurality of tap selecting switch contacts associated therewith for establishing selected points of connection between a line circuit conductor and a selected one of said taps, load circuit interrupting switches for interrupting the flow of load current through the tap selector switches during a tap changing operation prior to movement of a tap selector switch from one tap position to another and for establishing connection therethrough after movement to a new tap position, motive means for operating the tap changing mechanism from one tap position to another, and protective means responsive to a predetermined overload on the transformer for arresting operation of the last-named means during a tap changing operation.

2. In a tap changing equipment for transformers, a transformer winding having a plurality of taps and a plurality of tap selecting switch contacts associated therewith for establishing selected points of connection between a line circuit conductor and a selected one of said taps, load circuit interrupting switches for interrupting the flow of load current through the tap selector switches during a tap changing operation prior to movement of a tap selector switch from one tap position to another and for establishing connection therethrough after movement to the new tap position, an electric motor for operating the tap changing mechanism from one tap position to another, and a circuit interrupting switch responsive to a predetermined overload on the transformer for interrupting the operation of the motor.

3. In a tap changing equipment for transformers, a transformer winding having a plurality of taps and a plurality of tap selecting switch contacts associated therewith for establishing selected points of connection between a line circuit conductor and a selected one of said taps, load circuit interrupting switches for interrupting the flow of load current through the tap selector switches during a tap changing operation prior to movement of a tap selector switch from one tap position to another and for establishing connection therethrough after movement to the new tap position, motive means for operating. the tap changing mechanism from one tap position to' another, protective means responsive to a predetermined overload on the transformer for arresting operation of the last-named means during a tap changing operation, and means eflective upon operation of said protective means for continuing operation of said motive means until the load circuit interrupting switches have arrived at predetermined positions.

- 4. In a tap changing equipment for transformers, a transformer winding having a plurality of taps and a plurality of tap selecting switch contacts associated therewith for establishing selected points of connection between a line circuit conductor and a selected one of said taps, load circuit interrupting switches for interrupting the flow of load current through the tap selector switches during a tap changing operation prior to movement of a tap selector switch from one tap position to another and for establishing connection therethrough after movement to the new tap position, an electric motor for operating the tap changing mechanism from one tap position to another, a circuit interrupting switch responsive to a predetermined overload on the transformer for interrupting the operation of the motor, and means including locking contacts actuated by said electric motor for shunting said circuit interrupting switch upon starting of the motor to maintain the motor in operation until the load circuit interrupting switches have arrived at predetermined positions.

MAX SCHWAI'GER. 

